Apparatus in continuous casting machines having a reciprocating mold



Apr1l21, 1964 E. A. oLssoN 3,129,474

APPARATUS IN CONTINUOUS CASTING MACHINES HAVING A RECIPROCATING MOLDFiled Nov. 22. 1961 FgJ ERIK ALLAN 0LS`SON ATTORNEYS nited States Patent3,129,474 APPARATUS IN CONTINUUS CASTING MA- CHlNES HAVEN@ ARECIPRQCATING MOLD Erik Allan Olsson, Zurichstrasse 66, Kusnacht,Zurich, Switzerland Filed Nov. 22, 1961, Ser. No. 154,284 Claimspriority, application Sweden Jan. 3, 1961 2 Claims. (Ci. 22-57.2)

In continuous casting of metals, comprising non-ferrous metals andalloys as well as more particularly iron and ferrous alloys, the fluidmetal is supplied to one end of an open-ended mold which is made from amaterial having good thermal conductivity, e.g. copper. Due to thecooling action achieved by the mostly water-cooled mold, the metalsolidies in the marginal zone of the crosssection of the casting,whereupon the at least partly solidiled casting is withdrawn at theopposite end of the mold.

Within the mold there is formed a solid outer layer or shell on thecasting passing through the mold on account of its contact with thecooled mold wall. However, this contacts lasts only as long as thepressure of the fluid metal is able to force the solidified outer layeror shell into contact with the mold wall. When the solidified layer hasreached a certain thickness, the continued shrinkage of, eg., apolygonal section will cause initially the corner portions of thecasting to be disengaged from the mold wall, while the intermediate flatsurfaces are still for a certain period forced against the mold wall bythe action of the pressure of the iluid metal before they, too, losecontact with the wall. As soon as the contact of the casting with thewall ceases, the gas layer formed in the resulting clearance willrestrict the dissipation of heat and thereby the growth of thesolidified layer. In order that the partly solidified casting shall becapable of being withdrawn from the mold, however, the solid surfacelayer must have a certain strength so that it can withstand the sum ofall mechanical forces involved, including the head of the lluid metal inthe interior of the casting. The higher the rate of supply of fluidmetal to the mold, i.e. the higher the casting velocity chosenrelatively to a given section of the casting, the greater the amount ofheat removed per unit time must be in order that a solidified surfacelayer having the requisite strength shall be formed. The efficiency of acontinuous casting mold or the casting velocity which can be achieveddepends to a large extent on the heat transfer properties of the mold.The casting efhciency of a continuous casting mold can be improved byimparting to the mold a definite rhythmical reciproeating movement insuch a manner that the mold for a certain period of time accompanies themovement of the casting with at least approximately the same speed asthe casting, so that during this period a relative movement between themold and casting is prevented. Thereupon the mold is moved in adirection opposite to that of the casting back to the starting point.During the synchronous movement of the mold and the casting the effectof the friction forces is eliminated, wherefore the solidifying outerlayer at the weakest point immediately below the fluid metal surface isnot subjected to mechanical stresses.

It has been suggested to make the mold so short that the casting leavesthe mold immediately after it has been disengaged from the mold wall. Inpractice, however, this is not possible, because the length of the moldmust not be below the minimum necessary to make sure that if the castingspeed is increased briefly the zone of disengagement will not be belowthe mold which would inevitably result in a rupture in the solidifiedouter layer. On the other hand, it is also disadvantageous to extend themold far beyond the zone of disengagement, since practi- 3,129,474Patented Apr. 21, 1964 ICC cally no cooling action is achieved betweenthe disengagement zone and the lower end of the mold.

It will be seen from the above that the greatest danger of rupture onthe solidified outer layer is present at the exit of the casting fromthe mold. In normal conditions, the solidified outer layer of thecasting is suillciently strong at this point to withstand the mechanicalstresses referred to above, in particular the inner pressure caused bythe fluid metal. There is no absolute certainty, however, that rupturewill not occur since even the smallest fissure in the outer layer canreduce the strength to an impermissible degree. Several means ofreducing the danger of rupture have been proposed, one such proposalinvolving the provision of water-cooled elements at the outlet end ofthe mold, said cooling elements being kept pressed with a slightpressure toward the casting and serving to increase the strength in theouter layers of the casting through further indirect cooling and toprevent rupture by supporting the solidified outer layer externally.Immediately below the cooling elements direct cooling takes place bymeans of water under pressure as is usual in most continuous castingprocesses. In this subsequent cooling system there are usually provideda plurality of small guide rollers which also serve to prevent bulgingof the solidified outer layer by the action of the internal pressure ofthe unsolidifled metal. Considering the process in connection with areciprocating movement of the mold, it will be seen, however, that thecooling elements, which accompany the mold in such movement, in eachstroke expose a length of the casting corresponding at least to thelength of the stroke, which length of casting at that point isunsupported from the outside and the outer layer of which under somecircumstances has not yet obtained a suicient strength to withstand theinternal pressure of the fluid metal.

The object of this invention is to remove that disadvantage, theinvention being characterized substantially by one or more coolingelements provided at the exit end of the mold and movable independentlyof the mold, said cooling elements surrounding the casting withdrawnfrom the mold and cooling it to increase the thickness and consequentlythe strength of the outer layer solidified in the mold.

The invention will be explained more in detail below with reference tothe accompanying drawing, which diagrammatically illustrates anembodiment thereof, FIG- URES 1-5 illustrating the cooling process inlive stages during a complete stroke of the mold.

FIGURE l shows the first stage in which the mold 6 and the coolingelements 7 are in their starting position, i.e. the upper reversingposition, indicated at 8, of the stroke which is altogether designated9. The cooling water nozzles y10 and 11 which are provided around thecasting section and the cooling elements 7 and mold 6, are stationary asis also the subsequent cooling means 12 which also includes guidingrollers 13. The casting 14 is withdrawn at a continuous speed themagnitude of which is indicated by the arrow 15. In this startingposition the cooling members are immediately below the lower end of themold.

FIGURE 2 shows the second stage in which the mold 6 moves in thedirection of withdrawal of the casting 14 at a speed, which issubstantially equal to the velocity of withdrawal of the casting. Inthis stage, too, the cooling elements 7 move in the same direction butat a speed which is greater, e.g. twice the speed of the mold 6. Betweenthe mold and the cooling members there will be formed a gap 18 which isequal to the distance 19 traveled by the mold if the speed of thecooling members as indicated by the arrow 17 is twice the speed of themold (indicated by the arrow 16). lThe casting portion thus exposed issprayed with water from the nozzles 10.

In the third stage, illustrated in FIGURE 3, the cooling elements 7 havetraversed the entire distance 9 while the mold has moved only half thatdistance which means that the exposed portion 18 is doubled and issubjected to cooling water from the nozzles 11. In the fourth stageillustrated in FIGURE 4 the cooling elements 7 remain in the lowerposition 20, while the mold 6 is still moving down at a constant speed,whereby the exposed portion 18 is reduced while it is still subjected tocooling water from the nozzles 11.

At the end of the fth stage shown in FIGURE 5, the mold has caught upwith the cooling elements 7, whereby the casting is Iagain whollyenclosed. Thereupon, the mold and cooling elements return at a constantspeed to their starting positions (FIGURE l) and the process isrepeated.

Considering a casting section 21 during the stages described it will beseen that this best cooled section after the simultaneous return of themold and cooling elements to the upper end position 8 will beimmediately below the lower ends 22 of the cooling elements in case thecooling elements have a length which is at least as great as the stroke9 of the reciprocating movement. The solidified outer layer of thecasting section 23 which is exposed during the return movement andwherein the danger of damage is the greatest, due to the cooling by thecooling elements 7 and the direct cooling by the cooling water nozzles10 and 11, has increased in thickness to such an extent that a ruptureat this place is no longer to be feared in normal circumstances.

The invention is not limited to the embodiment shown and described whichcan be varied in many Ways without departing from the spirit and scopeof the invention.

I claim:

1. The combination with a continuous casting machine having areciprocating mold, of at least one cooling element `at the outlet endof the mold and movable independently of the mold, said cooling elementswholly enclosing a casting leaving the mold, means for moving saidcooling elements faster than the mold in the direction of casting toform a gap between the mold and the cooling elements, means for stoppingsaid cooling elements to close said gap, means for moving said mold andcooling elements together as a unit in the direction opposite saidcasting direction, and at least one cooling water nozzle positioned toproject cooling water onto a portion of a casting exposed by said gapduring said movement of the mold and the cooling elements in the castingdirection.

2. The method of casting comprising pouring a molten metal into one endof a reciprocating mold and continuously withdrawing partially solidiedmetal from the other end of the mold while wholly surrounding andengaging the entire peripheral surface of the cast metal at said otherend with at least one cooling element, moving said cooling element inthe casting direction at a speed greater than that of the mold to open agap between the mold and the cooling element, projecting a cooling fluidonto the cast metal in said gap, stopping said cooling element to closesaid gap, and returning said mold and cooling element together at thesame speed in the direction opposite the casting direction.

References Cited in the le of this patent UNITED STATES PATENTS2,726,430 Rossi Dec. 13, 1955 2,871,534 Wieland Feb. 3, 1959 2,895,190Bungeroth July 2l, 1959 FOREIGN PATENTS 44/1961 Sweden Jan. 3, 1961

1. THE COMBINATION WITH A CONTINUOUS CASTING MACHINE HAVING A RECIPROCATING MOLD, OF AT LEAST ONE COOLING ELEMENT AT THE OUTLET END OF THE MOLD AND MOVABLE INDEPENDENTLY OF THE MOLD, SAID COOLING ELEMENTS WHOLLY ENCLOSING A CASTING LEAVING THE MOLD, MEANS FOR MOVING SAID COOLING ELEMENTS FASTER THAN THE MOLD IN THE DIRECTION OF CASTING TO FORM A GAP BETWEEN THE MOLD AND THE COOLING ELEMENTS, MEANS FOR STOPPING SAID COOLING ELEMENTS TO CLOSE SAID GAP, MEANS FOR MOVING SAID MOLD AND COOLING ELEMENTS TOGETHER AS A UNIT IN THE DIRECTION OPPOSITE SAID CASTING DIRECTION, AND AT LEAST ONE COOLING WATER NOZZLE POSITIONED TO PROJECT COOLING WATER ONTO A PORTION OF A CASTING EXPOSED BY SAID GAP DURING SAID MOVEMENT OF THE MOLD AND THE COOLING ELEMENTS IN THE CASTING DIRECTION. 